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House keeping items - noise: First attempts at running the HA160D as DAC or preamp in my big rig caused a fat hum as soon as the Burson threaded into the signal path. This couldn't be cured with a floating ground*. The hum occurred already without a power cord plugged into the Burson. Whilst my ModWright KWA 100SE power amp has a ground-lift feature, this merely affected the hum's amplitude. It did not eliminate it. The original HA160 had suffered a ground loop issue but with certain sources only. Burson successfully addressed this with a subsequent circuit alteration when other users reported the same hum. Then it had only affected headphones of course. Now headphones were in the clear over all sources, be those iMac, iPod via Sieben Technology dock, Onkyo digital-direct dock or the digital and analog outputs of my Ancient Audio Lektor Prime. This noise was a 'downstream' rather than 'upstream' affair and occurred only when the Burson's pre-outs were used.

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* Switzerland's domestic 230V/50Hz power delivery isn't based on the Euro Schuko outlets. It uses a three-prong system with a Type J SEV 1011 wall plug instead that's unique to the country. I run CH-to-US wall adaptors, then US outlet multiplier boxes by Walker and Furutech with power cords terminated in American plugs. Floating a ground on these involves a so-called 3-to-2-prong cheater plug.

Wyred4Sound's ST500 amplifier was as noisy as the ModWright KWA-100SE. The low-power low-gain FirstWatt J2 reduced the noise to what most would consider normal for a large number of expensive valve amps. But preamps ought to be inaudible when no signal passes. My three in-house preamps—Esoteric C-03, ModWright DM 36.5, Bent Audio Tap X—all are. I finally lucked out. Even with the Burson's volume control fully open, my 25-watt Trafomatic Audio Kaivalya tube monos betrayed zero noise right at the tweeters. What caused the noise on three different amps but not the fourth I didn't know at this juncture. Burson reported back that they only ever experienced hum (with sources) when their interconnects were unshielded. I indeed run unshielded 5-meter links between preamp and amps. In two years I'd simply never had an issue with any preamp/amp combination. Hence I don't yet own any trouble-shooting shielded 5-meter equivalents.

"The preamp output of the 160D has higher impedance than some other designs. If the power amp also happens to have a higher input impedance, the combo will pick up interference in the air through an unshielded connection much like a TV antenna - especially a 5-meter long unshielded cable. Most branded interconnect cables should be shielded but if the customer is unwilling to part with his favorite pair of unshielded cables we can provide a free modification to lower the output impedance of the 160D here in Australia or at any of our authorized retailers like 32ohm Audio in Portland." To remove my suspicion that I suffered a ground loop instead, team Burson requested that I let them submit a 5-meter run of shielded interconnect. I accepted. Their cable proved that indeed I had not suffered a ground loop. My hum had arisen from long unshielded cables. Once shielded cables replaced them, the hum was gone.

Volume taper:
The 25wpc J2 also showed that with the Weiss DAC's four-step resistive trim pot set to just shy of 2V output voltage—max is above 5V—and with the Burson processing USB directly, its volume control at four clicks up from mute already generated standard room volumes in a space 5.5 meters wide by 12 meters long. I'd personally welcome a still shallower taper to maximize output gradations in the most-used range between background and civilized levels. With the same stepped pot controlling headphone micro voltages and line-level voltages for speaker drive, this decision is probably somewhat of an engineering challenge. "We have tried to design the gain level to suit most power amps while keeping performance at the top of our consideration. If a customer requests finer volume control when teaming it with a particular power amp, then again we can provide a simple free modification to lower the gain here in Australia or at the local retailer."

Digital data density: With my Weiss DAC2 as Firewire-to-S/PDIF converter progressively raising sample rates in its software panel, the Burson's S/PDIF input kept pace up to 176.4kHz. 192kHz didn't pass to cause muted outputs. The 24/96 USB input meanwhile acted curiously. Going through Amarra, native 96kHz and 192kHz files played back the first time at half and quarter speeds and transposed downward by one or two octaves. This made for very eerie effects but wasn't repeatable. In each subsequent session, Amarra would simply default to iTunes whenever I attempted to stream a 24/96 or 24/192 file. Amarra stubbornly identified the Burson as only 41100 USB and refused to stream files of higher data density. Trying to change iTunes' Audio Midi settings instead, the Burson's only selectable sample rates came up as 32000, 41100 and 48000Hz. As far as the iMac was concerned, the HA160D's USB input was limited to 48kHz. It failed to recognize any 24/96 capability.

John Delmo: "We are presently consulting with an external software expert who may have to design a software patch. If so he has indicated a turn-around time of one month. We'll inform you of the patch when it becomes available of course." Interestingly, pro-audio firms Benchmark Media and Lavry Engineering have gone on record that most modern DAC chips don't operate fast enough at 192kHz where they suffer significantly higher out-of-band noise than at 96kHz (John Siau of Benchmark cites a whopping 40dB advantage in stopband attenuation for 96kHz operation over 192kHz in fact).

For some context, the below screen capture from Linn Records shows how a 24-bit/96kHz file has five times the data density than its 16-bit/44.1kHz equivalent. 192kHz doubles it again. The Burson will handle up to 24/176.4 files over its coaxial port. For such files you'll simply need a USB/S-PDIF converter like the affordable M2Tech hiFace (or an equivalent Firewire/S-PDIF interface as Weiss makes).

Comparing the HA160D's S/PDIF and USB feeds, I heard no discernable differences. If anything, I occasionally thought USB more solid (probably imaginary but I curiously never favored the coaxial signal). Considering that the Weiss as D/D converter slaved the Burson to its own clock, it was obvious how the USB input was asynchronous itself and properly deslaved from the iMac.

HA160D vs. HA160: As expected when fed from a Sieben Technology dock each to merely require I reseat my fully loaded 160GB Classic iPod and T1 headphones, these stable mates were very closely matched. Owners of the original haven't suddenly devolved into 2nd-class citizen. If we disregard the added DAC feature, they should feel no urge to upgrade (not that such assurances ever prevented anyone).

That said, there were two consistent small differences. One, the D version had a bit more energy above the upper midrange. This meant more top-end sheen. With overcooked Pop albums or close-mic'd cymbals, this could quicken the onset of sizzle but on most material—particularly quality ECM, enja and m.a. level stuff—I thought it a worthwhile refinement. Not really noticeable with most acoustic music but obvious on artificially enhanced fare was that the D version pounded harder on slam beats. Since those occur mostly on club music, the glossier top was nicely counterbalanced for no slippage of the acoustic midpoint up or down.

The upshot was a slightly more energetic but just as well-balanced reading. It felt true then that the D version wasn't merely a functionally enhanced 160 but had been subtly tweaked. The question I can't answer is this: to add D/A conversion to the HA160, would your hard-earned $1.100 be spent better on the HA160D; or on the HA160 plus a $150 or $350 HRT Streamer II or II+ (requiring one extra analog interconnect)?

The two-box solution would actually take up a little less real estate since the D version is wider. It could also upgrade you to 24/192 asynchronous USB but remove the S/PDIF input, multiple outputs and preamp functionality. Without serious interest in hi-rez files, I'd probably fancy the single box from Oz more.